Extension rod for drill rods



Oct. 12, 1965 B. H. A. KARLSSON ETAI. 3,211,434-

EXTENSION ROD FOR DRILL RODS 2 Sheets-Sheet 1 Filed Oct. 30, 1963 Fig.2

Fig.1

Oct. 12, 1965 B. H. A. KARLSSON ETAL 3,211,484

EXTENSION ROD FOR DRILL RODS 2 Sheets-Sheet 2 Filed Oct. 30, 1963 6 L fk United States Patent 3,211,484 EXTENSION ROD FOR DRILL RODS BernhardHjalmar Adolf Karlsson and Gunnar Arne Gustafsson, both of Sandviken,Sweden, assignors to Sandvikens Jernverks Aktiebolag, Sandviken, Sweden,a corporation of Sweden Filed Oct. 30, 1963, Ser. No. 320,126 Claimspriority, application Sweden, Nov. 2, 1962, 11,779/62 1 Claim. (Cl.287--117) In drilling deep holes in earth or rock a drill rod is oftenused comprising a number of extension rods threaded at both ends andinterconnected by a coupling piece at each joint. In the use of suchthreaded extension rods it frequently occurs that the thread is worn outor damaged. In percussion drilling the rod breaks at the diminishedthreaded section because of fatigue stresses. Such damage or rupture ofthe threaded section permits further use of the extension rod afterre-threading the broken end. This re-threading is, however, difficult toperform at the place where the drill is used and the rod generally hasto be taken to a workshop for re-threading.

The present invention aims at an improvement in this respect bymanufacturing the extension rods with an extra threaded portion adjacentto the end thread and having the same length as the end thread. When theend thread breaks or is worn out it is only cut away and the extrathread forms the new end thread. The only operation needed is to cut offthe worn out thread portion and to finish the end surface so that therods have full end contact with each other at the joint. Theseoperations generally may be performed at the drilling site. The morecomplicated pre-threading is performed in advance at the factory inmaking the drills. This involves an increase of the manufacturing costbut a reduction of the total cost, as all the necessary threading isperformed in one step, when the rod is mounted in the threading machine.Further the cost for transporting the rod between the drilling site anda workshop for re-threading is eliminated. This contributes the furtheradvantage that the quantity of drill equipment necessary for a certainjob is reduced, as none of it has to be sent away for rethreading,thereby reducing also the investment costs and simplifying the transportproblem in isolated drilling sites.

Further details and advantages of the invention appear from thefollowing specification and the accompanying drawing in which FIG. 1 isan elevational view, partly in section of a joint of two extension rodshaving a circular cross section and external threads.

FIG. 2 is an elevational view of a joint of a hexagonal rod having anexternal thread.

FIG. 3 is an elevational View of a modification of the joint shown inFIG. 2.

FIG. 4 is an elevational view, partly in section of an embodiment withcircular rods having internal threads.

FIG. 1 shows two extension rods and 11 forming elements of a drill rodof the kind generally used for percussion drilling. The extension rodshave circular cross sections and are externally threaded by outerthreads 13 and 14 respectively and coupled together by a coupling sleeve12 having an internal thread 15. The rods abut against each other at theend surfaces 16 and 17 respectively, which should be plane andperpendicular to the drill axis in order to obtain full contact. This isvery important in percussion drilling, where great forces aretransferred between the rods and bad end surface contact causesrelatively great losses of drilling energy.

At the ends of the threads 13 and 14 that are remote from the ends ofthe rods there are unthreaded portions 18 and 19 respectively which formstops for the coupling sleeve and hold the sleeve in a position that issymmetric with relation to the abutment surfaces 16 and 17. The lengthof the coupling sleeve is less than the total length of the threads 13and 14, so that there is enough room for the coupling sleeve between thestops 18 and 19 in order to ensure the full abutment between the ends 16and 17. Beyond the abutments 18 and 19 each of the extension rods has asecond thread 20 and 21 respectively having the same length as thethreads 13 and 14. The abutment portions 18 and 19 thus form a shortseparate portion between the threads. With extension rods having acircular cross section as in the present embodiment, it is suitable toprovide the rods with wrench grips 22 and 23 respectively in order tofacilitate the turning of the rods when they are being screwed into thecoupling sleeve. The abutments 18 and 19 have preferably the same crosssection as the rods and they can be provided with similar wrench gripsif desired. 24 is a flushing channel.

If for instance the thread marked 14 breaks, the rod 11 is cut otf atthe section AA and the end is finished to a plane surface that isperpendicular to the drill axis. As the thread 21 is similar to thediscarded thread 14, the rod 11 can now be connected to the couplingsleeve by the thread 21. The rod 10 can be cut off and reconnected inthe same way using the thread 20 for the connection.

The portions 18 and 19 are suitably integral with the rod and have thesame cross section as the rod, which means that in making the twothreaded portions these portions 18 and 19 are left unworked between thethreads. It is also possible to make a continuous thread having thelength of the two threads together but in this case a separate abutmentstop is placed on the thread in order to determine the position of thecoupling sleeve.

In FIG. 2 is shown a similar joint for hexagonal rods. The extension rod30 is screwed to a coupling sleeve 31 and has at its end a thread withinthe sleeve (not shown). Adjacent to said end thread is an abutmentportion 32 having the same hexagonal cross section as the rod andadjacent to the abutment portion 32 there is a second thread 33.

FIG. 3 shows an extension rod 34 which is slightly modified incomparison with FIG. 2. The sleeve 35 is attached to an end thread (notshown), and the abutment stop 36 has a circular cross section. At theend of the second thread 37 there is a short portion 38 having acircular cross section.

The invention can also be used for extension rods having internalthreads as shown in FIG. 4. Two rods 40 and 41 forming elements of adrill rod are provided with axial end bores having internal threads 42and 43 respectively close to the open ends of the bores and secondthreads 44 and 45 respectively close to the bottoms of the bores.Between the two thread portions 42-44 and 43-45 in each bore there is anunthreaded portion 46 and 47 respectively. The rods are coupled togetherby an externally threaded tap 48. When the threads 42 and 43 or eitherof them is worn out or otherwise made unusable the rods are cut off atthe cross sections BB and CC, the abutment surfaces are finished, andthe threads 44 and 45 are used for coupling the rods together.

The invention is especially useful for common percussion drill extensionrods having a thread on each end but can also be used for such parts ofthe drill rod that have a thread only at one end, as a drill rod havinga drill bit integral therewith at one end. It is of course possible alsoto use the invention in connection with other kinds of drills as rotarydrills. Other obvious variations of the described embodiments can bemade within the scope of the following claim.

We claim:

In a drill rod, an extension rod having a long unthreaded portioncomprising the main and central part of the extension rod, at least oneend portion being externally threaded and having two consecutive threadshaving the same pitch, length and diameter, said threads being separatedby an integral short unthreaded portion having a cross-sectional areasubstantially at least equal to the cross-sectional area of said longunthreaded portion, said long unthreaded portion and said shortunthreaded portion each having an external dimension at least equal tothe external dimension of said threads, the outermost of said threadsextending to the end of said extenison rod and being adapted to receivean internally threaded sleeve for coupling said extension rod to asecond extension rod, the end surface of said extension rod beingadapted to abut against a similar surface ,on said second extension rod,said short unthreaded portion forming an abutment stop for said sleevewhen screwed onto said outermost thread, the innermost of said threadsbeing adapted to receive said sleeve for said coupling purpose aftercutting off said outermost thread together with said short unthreadedportion, said long unthreaded portion serving as an abutment stop forsaid sleeve when screwed onto said innermost thread.

References Cited by the Examiner UNITED STATES PATENTS 1,185,846 6/16Simpson 285-4 x 1,344,032 6/20 Greenfield 285-390 1,642,183 9/2'7Thurston 287-117 1,712,108 5/29 Goeller 287---114 2,289,785 7/42Hutchison 8561 2,611,066 9/52 Freeman 851 FOREIGN PATENTS 1,183,318 1/59France.

CARL W. TOMLIN, Primary Examiner.

THOMAS F. CALLAGHAN, Examiner.

